Early cortical GABAergic interneurons determine the projection patterns of L4 excitatory neurons.

During cerebral cortex development, excitatory pyramidal neurons (PNs) establish specific projection patterns while receiving inputs from GABAergic inhibitory interneurons (INs). Whether these inhibitory inputs can shape PNs' projection patterns is, however, unknown. While layer 4 (L4) PNs of the primary somatosensory (S1) cortex are all born as long-range callosal projection neurons (CPNs), most of them acquire local connectivity upon activity-dependent elimination of their interhemispheric axons during postnatal development. Here, we demonstrate that precise developmental regulation of inhibition is key for the retraction of S1L4 PNs' callosal projections. Ablation of somatostatin INs leads to premature inhibition from parvalbumin INs onto S1L4 PNs and prevents them from acquiring their barrel-restricted local connectivity pattern. As a result, adult S1L4 PNs retain interhemispheric projections responding to tactile stimuli, and the mice lose whisker-based texture discrimination. Overall, we show that temporally ordered IN activity during development is key to shaping local ipsilateral S1L4 PNs' projection pattern, which is required for fine somatosensory processing.

Validation of the Spanish version of DYsphagia in MUltiple Sclerosis questionnaire (DYMUS).

BACKGROUND: Dysphagia is a common symptom in multiple sclerosis that can occur even early in the disease course and can lead to serious complications. Early recognition and treatment can promote comfort, safety and optimal nutritional status. Few dysphagia rating scales are available in Spanish. The aim of this study was to translate the Dysphagia in Multiple Sclerosis Questionnaire (DYMUS) into Spanish and to validate it. METHODS: Forward and backward translation method was used to translate the original English version of DYMUS into Spanish. A pilot-study with 10 PwMS was carried on in order to improve the intelligibility of the instrument, comprehensibility and content validity of the questionnaire. The questionnaire was filled out by 100 PwMS who were asked a dichotomous question on their swallowing ("Do you have swallowing troubles?"). Descriptive data are presented as median and quartiles for continuous variables and frequency and percentage for categorical ones. Internal consistency reliability was estimated by Cronbach's alfa. Test-retest reliability was estimated by intraclass correlation coefficient. Concurrent validity with a speech and language therapy assessment (SLT-A) was measured with the weighted kappa statistic for the concordance for both dysphagia type and degree categories. Confirmatory factor analysis by means of structural equation models was used to verify the two-factor (solids and liquids) structure of the DYMUS questionnaire. As the goodness of fit evaluation was poor, an additional exploratory factor analysis was carried out. RESULTS: Internal consistency was high. The globus sensation question and the weight loss questions (item 3 and 10) are the least specific with dysphagia symptomatology so they are worst correlated with the sum of the others (item-rest correlation, 0.243 and 0.248, respectively). The test-retest reliability of the DYMUS among 40 patients using ICC was 0.75 (95% CI 0.57 - 0.86). Concurrent validity with SLT-A was poor (weighted kappa 0.37 for dysphagia type and 0.38 for dysphagia degree). The DYMUS questionnaire detected three times more dysphagia (53% versus 17%) than the dichotomous question. Confirmatory factors analysis failed to confirm the bidimensional structure (solid and liquid items) often reported in other validation studies. The subsequent exploratory factor analysis also identified two factors, but with poor interpretability. CONCLUSION: DYMUS-SP scale is not a sufficiently useful scale to detect dysphagia in PwMS due to the poor concurrent validity and the probable overdiagnosis of the condition; however, it can be helpful as a screening tool when combined with other measures.

Role of Nrp1 in controlling cortical inter-hemispheric circuits.

Axons of the corpus callosum (CC) mediate the interhemispheric communication required for complex perception in mammals. In the somatosensory (SS) cortex, the CC exchanges inputs processed by the primary (S1) and secondary (S2) areas, which receive tactile and pain stimuli. During early postnatal life, a multistep process involving axonal navigation, growth, and refinement, leads to precise CC connectivity. This process is often affected in neurodevelopmental disorders such as autism and epilepsy. We herein show that in mice, expression of the axonal signaling receptor Neuropilin 1 (Nrp1) in SS layer (L) 2/3 is temporary and follows patterns that determine CC connectivity. At postnatal day 4, Nrp1 expression is absent in the SS cortex while abundant in the motor area, creating a sharp border. During the following 3 weeks, Nrp1 is transiently upregulated in subpopulations of SS L2/3 neurons, earlier and more abundantly in S2 than in S1. In vivo knock-down and overexpression experiments demonstrate that transient expression of Nrp1 does not affect the initial development of callosal projections in S1 but is required for subsequent S2 innervation. Moreover, knocking-down Nrp1 reduces the number of S2L2/3 callosal neurons due to excessive postnatal refinement. Thus, an exquisite temporal and spatial regulation of Nrp1 expression determines SS interhemispheric maps.

Development and plasticity of the corpus callosum.

The corpus callosum (CC) connects the cerebral hemispheres and is the major mammalian commissural tract. It facilitates bilateral sensory integration and higher cognitive functions, and is often affected in neurodevelopmental diseases. Here, we review the mechanisms that contribute to the development of CC circuits in animal models and humans. These species comparisons reveal several commonalities. First, there is an early period of massive axonal projection. Second, there is a postnatal temporal window, varying between species, in which early callosal projections are selectively refined. Third, sensory-derived activity influences axonal refinement. We also discuss how defects in CC formation can lead to mild or severe CC congenital malformations.